In a first improvement disclosed in the above-mentioned parent applications, a test assembly is disposed in a separate test channel in a safe, e.g. shielding block. A connector tube connects at a first end to the test channel and at a second end to a connector disposed in the guide tube. Thus, a juncture is formed at the connector between the guide tube and the connector tube. A test assembly transport thread (cable) is attached at one end to the test assembly and at another end to a test assembly drive means for driving the test assembly from the test channel, through the connector tube and connector, and toward the second end of the guide tube. In this arrangement, the source assembly and the test assembly are alternatingly drivable toward the second end of the guide tube. A detector means is provided for detecting the presence of a test assembly or the source assembly in the guide tube between the juncture and the second end of the guide tube.
Thus, in this arrangement, the test assembly is driven through the connector tube and guide tube and past the detector, which is generally at the juncture between the connector tube and the guide tube. The detector will determine when the test assembly passes that juncture. Since the guide tube between the juncture and the site of intended therapy will be a common path for both the test assembly and the source assembly, accurately measuring the excursion of the test assembly from the detector to the site of intended therapy (confirmed by X-ray or the like) will give a very precise measurement of the excursion necessary for the source assembly once that source assembly also passes the detector and into the common pathway guide tube. The guide tube can remain essentially in place on the patient during both when the test assembly is operated and when the source assembly is operated, and, hence, disturbing the common pathway guide tube is not necessary. This gives a very precise positioning of the source assembly for effective radiation therapy and is a substantial improvement over the prior art.
In the second improvement disclosed in the parent applications, the test assembly may, in fact, be an LDR source. With this change, the LDR source may be used for the test assembly or may be used for radioactive therapy, although a single LDR source would have very limited practical clinical application for treating cancers. However, the LDR source can be effectively used as a test for radiation. For example, an LDR source may be placed in an applicator for treating uterine cancer (at a position intended to be occupied by a HDR source during treatment), and a radiation probe can be placed in the rectum to measure the radiation of the LDR source at the rectum (which should be the minimum possible). This radiation can then be ratioed to the radiation which will be received by the rectum when the HDR source is at that position. This can be of considerable assistance to the physician in determining and confirming proper positions for the HDR source.
In another aspect of the parent applications, in order to allow multiple sites of intended therapy to be serviced by a single machine, an indexer means, which is known to the art, may be disposed between the juncture (the juncture of the guide tube and the connector tube) and the second end of the guide tube so as to provide a plurality of branched guide tubes extending from the indexer to a plurality of sites of intended therapy. With this arrangement, for example, the correct positioning of the HDR source in any one of the branched guide tubes may be determined by using the LDR source as the test assembly, as described above, and after that correct positioning is determined, the HDR source is serially passed through each of the plurality of guide tubes, in turn, so that the source is positioned serially at different sites of intended therapy around and about the malignancy. By choosing a particular residence time of the HDR source at each position in each of the branched guide tubes, the total radiation provided by the HDR source, with a short residence time in each position, can be somewhat equivalent to the radiation provided by a plurality of LDR sources with much longer residence times. In serially passing the HDR source through the plurality of branched guide tubes, a wide area in and around the malignancy can be radiated to effect similar radiation to that which would have been achieved with a conventional LDR machine using a plurality of LDR sources.